/Engine/Source/Editor/UnrealEd/Public/Toolkits/AssetEditorToolkit.h
Called when a toolkit requests an overlay widget to be added to the viewport. Not relevant in the absence of a viewport.
virtual void AddViewportOverlayWidget ( [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > InViewportOverlayWidget )